1. Field of the Invention
The present invention relates to an optical disc device configured to be able to visually record images: by using an optical disc in which an image recording layer is provided on a label side, which is a back face of a signal side irradiated with laser beam for reading out signals recorded in a signal recording layer; and by irradiating the laser beam to the image recording layer.
2. Description of the Related Art
Optical disc devices capable of a signal reading operation and a signal recording operation by irradiating laser beam radiated from an optical pickup device to a signal recording layer of an optical disc is widely used.
For example, in the optical disc devices using optical discs called as CD and DVD, there is a type that is configured to be able not only to read out a recorded data signal but also to record a data signal in the optical disc.
When these optical discs recorded as above are to be put in order, contents of the recorded data are noted in marker pens or the like on label sides of the optical discs such that the contents of the data signal personally recorded in the optical discs can be known. However, with such a method, the note is hand-written, which is not good in appearance, and since it requires writing instruments, it is very inconvenient. Alternatively, such a method is employed that an image is printed on a label side by a printer, but it requires a special kind of printers, which is not practical.
As a method to solve those problems, such an art has been developed recently that an image recording layer is provided on a label side, which is a back face of an optical disc, and that an image is recorded as visible information by irradiating laser beam to the image recording layer. In this art, with a signal recorded in the signal recording layer being ready to be reproduced, the optical disc is loaded on a turntable upside down and image data desired by a user is inputted and processed, while a driving signal supplied to a laser diode by an action of an image forming driving circuit is changed and a spot position of the laser beam is controlled such that the image is recorded in the image recording layer provided on the label side (See Japanese Patent Laid-Open No. 2005-93052 and Japanese Patent Laid-Open No. 2005-216468).
The art described in Japanese Patent Laid-Open No. 2005-93052 is configured that a gain of a driving device when an objective lens is driven and displaced in the radial direction of the optical disc based on a reference pattern arranged on the innermost circumferential position of the optical disc, that is, a driving displacement amount to the driving signal value is obtained, and by controlling the displacing operation of the objective lens in the radial direction of the optical disc based on the obtained gain, a spot position of the laser beam for recording an image in the image recording layer provided on the optical disc is controlled.
The reference pattern is a serrated state inclined linearly in the radial direction of the optical disc, for example. An operation to obtain the above gain is achieved by moving the spot of the laser beam to a position forming the reference pattern while the optical disc is rotated with a constant angular speed. From a duty ratio of a reflectance ratio detected when the spot scans the reference pattern, a spot position (radial position) in the radial direction is recognized. Several of the radius positions are sampled while the spot position is displaced in the radial direction of the optical disc within a range of the reference pattern, and sampled radius positions and a value of the driving signal supplied to a tracking coil displacing the objective lens in the radial direction at that time are stored in memory means as table data any time. And with the radius position of each sample and the driving signal value stored in the memory means as a coordinate value, a straight line most matching all the coordinate values, that is, a relation between the driving signal value and the driving displacement amount is obtained. The inclination of this straight line is obtained and set as a gain of the tracking coil for displacing the objective lens when the spot of the laser beam is driven and displaced in the radial direction of the optical disc.
Recently, in addition to the above-mentioned optical discs called as CD and DVD, an optical disc using a blue laser beam with a wavelength of approximately 400 nm as recording/reproducing laser beam (hereinafter referred to as a next-generation DVD) is standardized, and commercialization is being promoted. When the next-generation DVD is put into commercial use, optical disc devices which can use all the optical discs including the existing CD and DVD and the next-generation DVD are expected to be commercialized.
In this case, an optical pickup device capable of recording and reproducing operations of a signal from all the optical discs will be needed. In such an optical pickup device, there can be a method of incorporating two lenses of an objective lens for the CD and DVD and an objective lens for the next-generation DVD in the optical pickup device (See Japanese Patent Laid-Open No. 9-212905 and Japanese Patent Laid-Open No. 2001-344803).
With the optical pickup device in which two objective lenses are incorporated, the objective lenses can be arranged side by side in a direction crossing the radial direction of the optical disc, but in this case, if the two objective lenses are arranged such that one of them is moved on the same radius of the optical disc, the other objective lens will be moved along the radius of the optical disc at a position separated from that radius by a given distance. In this case, a direction of a signal track projected onto a photodetector via the objective lens deviated from the radius of the optical disc is deviated as this objective lens is moved toward the outer circumference side from the inner circumference side of the optical disc. As a result, there is a problem in the optical pickup device with this configuration that the signal recording and reproducing operations with high accuracy is not possible.
As a method to solve the above problem, there is a method of arranging two objective lenses side by side in the radial direction of the optical disc. In an optical pickup device with this configuration, when an objective lens arranged outside in the two objective lenses is moved to the innermost circumferential position of the optical disc, the objective lens arranged on the inner circumference side is moved to the further inner circumference side than that position. If the two objective lenses are arranged side by side in the radial direction of the optical disc as above, a clearance between the objective lens arranged on the inner circumference side of the optical disc and the turntable on which the optical disc is mounted becomes a problem. Such a problem can be solved by reducing the size of the two lenses or by devising the shape of a lens holder.
With an optical disc called as a blue-ray disc, for which commercialization is being promoted as one of the next-generation DVD, the innermost circumferential position of a data region is shifted to the inner circumference side as compared with the other optical discs. Therefore, in order to cope with the clearance problem from the turntable on which the optical disc is mounted, it is more advantageous that the objective lens for the blue-ray disc is arranged on the inner circumference side of the optical disc.
In an optical disc device including an optical pickup device in which: the objective lens for the blue-ray disc, that is, the objective lens for the next-generation DVD is arranged on the inner circumference side of the optical disc; and the objective lens for CD and DVD is arranged on the outer circumference side, when an image is recorded on the label side of the optical disc, the image recording layer is arranged on the surface of the label side for all the optical discs.
Therefore, the recording operation of an image signal to the label side can be carried out by laser beam irradiated from the objective lens for CD and DVD even for the optical disc of the next-generation DVD standard. And in this case, it may be so configured that the laser beam from the objective lens for the next-generation DVD arranged on the inner circumference side is irradiated the reference pattern provided on the inner circumference side of the optical disc so as to carry out the reading operation of data for image recording and control.
In the case of the above operation, if a distance between the objective lens for the next-generation DVD arranged on the inner circumference side and the objective lens for CD and DVD arranged on the outer circumference side is not accurate, the image recording operation with accuracy is not possible. In the optical pickup device, the objective lens for the next-generation DVD and the objective lens for CD and DVD are securely mounted to a lens holder, but the distance can not be as being set due to a mounting error.